Development of Prototype Quality Assurance Procedure for Blood Irradiator Using Glass Dosimeter Jig / 의학물리

For the purpose of quality assurance (QA) of the blood irradiator, QA programs for daily, monthly, and yearly were developed. For daily tests, simple items for basically operating the machine are recommended. For monthly and yearly tests, the measurement of dose to assure the dose delivery system are performed by a dosimetry devices (Glass dosimeter jig) developed in this study. The QA program is practical for clinical environment.

Absorbed Dose Determination for a Biological Sample Irradiated by Gamma Rays from a Cs-137 Source / 의학물리

In this study the dosimetric evaluation for a biological sample irradiated by gamma rays from Cs-137 irradiator (Gamma Irradiator, Chiyoda Technol Co., Japan) was performed for radiobiological experiment. A spherical water with a diameter of 3 cm was assumed as a biological sample. The absorbed dose were determined by the air kerma based dosimetric calculation system. The theoretical and Monte Carlo calculations (MCNPX) were performed and compared to evaluate measured air kerma and determined absorbed dose respectively. As a result of comparison with theoretical calculation, the measured air kerma was in good agreement within 3.1% at the distance of 100 and 200 cm from the source. In comparison with Monte Carlo results the determined absorbed dose along the central axis was in good agreement within 1.9% and 3.7% at 100 cm and 200 cm respectively. Although the preliminary results were obtained in this study these results were used as a basis of dosimetric evaluation for radiobiological experiment. Extended study will be performed to evaluate the dose in various conditions of biological samples.

Study on the Evaluation of TRS-398 Quality Factors with Central Electrode Corrections for Small Cylindrical Chambers / 의학물리

The quality factors (kQ,Q0) were evaluated by appling the results recently studied for the effect of central electrode in TRS-398 protocol. The PTW-31010 and IBA-CC13 chambers were used in this study. The quality factors were calculated as a function of beam quality for high energy electron and photon beams and compared with data currently used in TRS-398 protocol. In the PTW-31010 chamber using aluminium electrode, appling the new central electrode collections, the quality factors were 0.4% and 0.9% higher than current TRS-398 data for high energy photon and electron beams respectively. In the IBA-CC13 chamber using C-552 electrode, there are no variations in quality factors compared to TRS-398 data currently used.

Multi-institutional Comparison of Intensity Modulated Radiation Therapy (IMRT) Planning Strategies and Planning Results for Nasopharyngeal Cancer

The intensity-modulated radiation therapy (IMRT) planning strategies for nasopharyngeal cancer among Korean radiation oncology facilities were investigated. Five institutions with IMRT planning capacity using the same planning system were invited to participate in this study. The institutions were requested to produce the best plan possible for 2 cases that would deliver 70 Gy to the planning target volume of gross tumor (PTV1), 59.4 Gy to the PTV2, and 51.5 Gy to the PTV3 in which elective irradiation was required. The advised fractionation number was 33. The planning parameters, resultant dose distributions, and biological indices were compared. We found 2-3-fold variations in the volume of treatment targets. Similar degree of variation was found in the delineation of normal tissue. The physician-related factors in IMRT planning had more influence on the plan quality. The inhomogeneity index of PTV dose ranged from 4 to 49% in Case 1, and from 5 to 46% in Case 2. Variation in tumor control probabilities for the primary lesion and involved LNs was less marked. Normal tissue complication probabilities for parotid glands and skin showed marked variation. Results from this study suggest that greater efforts in providing training and continuing education in terms of IMRT planning parameters usually set by physician are necessary for the successful implementation of IMRT.

Commissioning of a micro-MLC (mMLC) for Stereotactic Radiosurgery / 의학물리

The 4 bank mico-MLC (mMLC; Acculeaf, Direx, Isral) has been commissioned for clinical use of linac based stereotactic radiosurgery. The geometrical parameters to control the leaves were determined and comparisons between measured and calculated by the calculation model were performed in terms of absolute dose (cGy/100 MU). As a result of evaluating calculated dose for various field sizes and depths of 5 and 10 cm in water in the geometric condition of fixed SSD (source to surface distance) and fixed SCD (source to chamber distance), most of differences were within 1% for 6 MV and 15 MV x-rays. The penumbral widths at the isocenter were approximately evaluated to 0.29~0.43 cm depending on the field size for 6 MV and 0.36~0.51 cm for 15 MV x-rays. The average transmission and leakage for 6 MV and 15 MV x-rays were 6.6% and 7.4% respectively in single level of leaves fully closed. In case of dual level of leaves fully closed the measured transmission is approximately 0.5% for both 6 MV and 15 MV x-rays. Through the commissiong procedure we could verify the dose characteristics of mMLC and approximately evaluate the error ranges for treatment planning system.

Comparative Analysis of Patterns of Care Study of Radiotherapy for Esophageal Cancer among Three Countries: South Korea, Japan and the United States / 대한방사선종양학회지

PURPOSE: For the first time, a nationwide survey of the Patterns of Care Study (PCS) for the various radiotherapy treatments of esophageal cancer was carried out in South Korea. In order to observe the different parameters, as well as offer a solid cooperative system, we compared the Korean results with those observed in the United States (US) and Japan. MATERIALS AND METHODS: Two hundreds forty-six esophageal cancer patients from 21 institutions were enrolled in the South Korean study. The patients received radiation theraphy (RT) from 1998 to 1999. In order to compare these results with those from the United States, a published study by Suntharalingam, which included 414 patients [treated by Radiotherapy (RT)] from 59 institutions between 1996 and 1999 was chosen. In order to compare the South Korean with the Japanese data, we choose two different studies. The results published by Gomi were selected as the surgery group, in which 220 esophageal cancer patients were analyzed from 76 facilities. The patients underwent surgery and received RT with or without chemotherapy between 1998 and 2001. The non-surgery group originated from a study by Murakami, in which 385 patients were treated either by RT alone or RT with chemotherapy, but no surgery, between 1999 and 2001. RESULTS: The median age of enrolled patients was highest in the Japanese non-surgery group (71 years old). The gender ratio was approximately 9:1 (male:female) in both the Korean and Japanese studies, whereas females made up 23.1% of the study population in the US study. Adenocarcinoma outnumbered squamous cell carcinoma in the US study, whereas squamous cell carcinoma was more prevalent both the Korean and Japanese studies (Korea 96.3%, Japan 98%). An esophagogram, endoscopy, and chest CT scan were the main modalities of diagnostic evaluation used in all three countries. The US and Japan used the abdominal CT scan more frequently than the abdominal ultrasonography. Radiotherapy alone treatment was most rarely used in the US study (9.5%), compared to the Korean (23.2%) and Japanese (39%) studies. The combination of the three modalities (Surgery+RT+Chemotherapy) was performed least often in Korea (11.8%) compared to the Japanese (49.5%) and US (32.8%) studies. Chemotherapy (89%) and chemotherapy with concurrent chemoradiotherapy (97%) was most frequently used in the US study. Fluorouracil (5-FU) and Cisplatin were the most preferred drug treatments used in all three countries. The median radiation dose was 50.4 Gy in the US study, as compared to 55.8 Gy in the Korean study regardless of whether an operation was performed. However, in Japan, different median doses were delivered for the surgery (48 Gy) and non-surgery groups (60 Gy). CONCLUSION: Although some aspects of the evaluation of esophageal cancer and its various treatment modalities were heterogeneous among the three countries surveyed, we found no remarkable differences in the RT dose or technique, which includes the number of portals and energy beams.

Accuracy Evaluation of Treatment Planning System Using Irregular-surface Water Phantom / 의학물리

We evaluated on the calculation accuracy of treatment planning system (TPS) with phantom having convex and concave surface. The TPS is Eclipse (Varian, USA) using both algorithms AAA and PBC for photon dose calculations. PBC algorithms have three corrections of Batho, modified Batho (M-Batho), and equivalent TAR (E-TAR). The field sizes were 10x10 cm2 and 20x20 cm2, and MLC-shaped fields for these fields. We measured doses at three depths 5, 10 and 15 cm in phantom of SSD=90 cm in the condition of inserted farmer chamber. For given conditions, we have calculated dose with these algorithms and compared them with measured doses. In AAA the calculated doses (dose/MU) were agreed to measured doses within +/-1% in flat and convex surface and were under estimated with -1.9% maximum in concave surface. In PBC the calculated doses were over estimated with +1.7% and +4.1% respectively in flat and convex surface and the differences were from -3.1% to +2.1% in concave surface. In comparison of criteria from AAPM and IAEA reports, and statistical analysis for these results, it is found that the AAA's results are in good agreement with measured values and the M-Batho's results are generally good agreed with measured values among PBC algorithms.

Effect of Transverse Magnetic Field on Dose Distribution of High Energy Electron Beam / 의학물리

In this work we have measured the dose distribution and the percent depth dose of 20 MeV electron beam using the X-OMAT films in order to verify the effects of transverse magnetic field on high energy elecrtron beam in a phantom. The result shows about 30% increase of the percent depth dose at 4.5 cm depth under the transverse magnetic field of 1.5 Tesla at 7.5 cm depth. We have verified that these were in an agreement with other theoretical results.

Monte Carlo Calculation on the Dose Modulation Using Dynamic Magnetic Fields for 10 MV X-rays / 의학물리

Monte Carlo calculations were performed to demonstrate the dose modulation with dynamic magnetic fields in phantom. The goal of this study is to obtain the uniform dose distributions at a depth region as a target on the central axis of photon beam under moving transverse magnetic field. We have calculated the depth dose curves for two cases of moving magnetic field along a depth line, constant speed and optimal speed. We introduced step-by-step shift and time factor of the position of the electromagnet as an approximations of continuous moving. The optimal time factors as a function of magnetic field position were calculated by least square methods using depth dose data for static magnetic field. We have verified that the flat depth dose is produced by varying the speed of magnetic field as a function of position as a results of Monte Carlo calculations. For 3 T magnetic field, the dose enhancement was 10.1% in comparison to without magnetic field at the center of the target.

Preliminary Report of the 1998~1999 Patterns of Care Study of Radiation Therapy for Esophageal Cancer in Korea / 대한방사선종양학회지

PURPOSE: For the first time, a nationwide survey in the Republic of Korea was conducted to determine the basic parameters for the treatment of esophageal cancer and to offer a solid cooperative system for the Korean Pattern of Care Study database. MATERIALS AND METHODS: During 1998~1999, biopsy-confirmed 246 esophageal cancer patients that received radiotherapy were enrolled from 23 different institutions in South Korea. Random sampling was based on power allocation method. Patient parameters and specific information regarding tumor characteristics and treatment methods were collected and registered through the web based PCS system. The data was analyzed by the use of the Chi-squared test. RESULTS: The median age of the collected patients was 62 years. The male to female ratio was about 91 to 9 with an absolute male predominance. The performance status ranged from ECOG 0 to 1 in 82.5% of the patients. Diagnostic procedures included an esophagogram (228 patients, 92.7%), endoscopy (226 patients, 91.9%), and a chest CT scan (238 patients, 96.7%). Squamous cell carcinoma was diagnosed in 96.3% of the patients; mid-thoracic esophageal cancer was most prevalent (110 patients, 44.7%) and 135 patients presented with clinical stage III disease. Fifty seven patients received radiotherapy alone and 37 patients received surgery with adjuvant postoperative radiotherapy. Half of the patients (123 patients) received chemotherapy together with RT and 70 patients (56.9%) received it as concurrent chemoradiotherapy. The most frequently used chemotherapeutic agent was a combination of cisplatin and 5-FU. Most patients received radiotherapy either with 6 MV (116 patients, 47.2%) or with 10 MV photons (87 patients, 35.4%). Radiotherapy was delivered through a conventional AP-PA field for 206 patients (83.7%) without using a CT plan and the median delivered dose was 3,600 cGy. The median total dose of postoperative radiotherapy was 5,040 cGy while for the non-operative patients the median total dose was 5,970 cGy. Thirty-four patients received intraluminal brachytherapy with high dose rate Iridium-192. Brachytherapy was delivered with a median dose of 300 cGy in each fraction and was typically delivered 3~4 times. The most frequently encountered complication during the radiotherapy treatment was esophagitis in 155 patients (63.0%). CONCLUSION: For the evaluation and treatment of esophageal cancer patients at radiation facilities in Korea, this study will provide guidelines and benchmark data for the solid cooperative systems of the Korean PCS. Although some differences were noted between institutions, there was no major difference in the treatment modalities and RT techniques.

Development of Independent Target Approximation by Auto-computation of 3-D Distribution Units for Stereotactic Radiosurgery / 의학물리

The stereotactic radiosurgery (SRS) describes a method of delivering a high dose of radiation to a small target volume in the brain, generally in a single fraction, while the dose delivered to the surrounding normal tissue should be minimized. To perform automatic plan of the SRS, a new method of multi-isocenter/shot linear accelerator (linac) and gamma knife (GK) radiosurgery treatment plan was developed, based on a physical lattice structure in target. The optimal radiosurgical plan had been constructed by many beam parameters in a linear accelerator or gamma knife-based radiation therapy. In this work, an isocenter/shot was modeled as a sphere, which is equal to the circular collimator/helmet hole size because the dimension of the 50% isodose level in the dose profile is similar to its size. In a computer-aided system, it accomplished first an automatic arrangement of multi-isocenter/shot considering two parameters such as positions and collimator/helmet sizes for each isocenter/shot. Simultaneously, an irregularly shaped target was approximated by cubic structures through computation of voxel units. The treatment planning method by the technique was evaluated as a dose distribution by dose volume histograms, dose conformity, and dose homogeneity to targets. For irregularly shaped targets, the new method performed optimal multi-isocenter packing, and it only took a few seconds in a computer-aided system. The targets were included in a more than 50% isodose curve. The dose conformity was ordinarily acceptable levels and the dose homogeneity was always less than 2.0, satisfying for various targets referred to Radiation Therapy Oncology Group (RTOG) SRS criteria. In conclusion, this approach by physical lattice structure could be a useful radiosurgical plan without restrictions in the various tumor shapes and the different modality techniques such as linac and GK for SRS.

Study for Multi Channel Radiation Detector Using of Microfilm and Carbon Electrode / 의학물리

We have designed the multi channel detector for the quality assurance of clinical photon beams. The detector was composed of solid phantom inserted by six plane-parallel ionization chambers at different depth. The chamber as a mini plane parallel chamber was made of carbon coated microfilms. In this study the electrical characteristics of the six chambers in the solid phantom were evaluated using 6 MV photon beam. The leakage currents were less than 0.5 pA, reproducibility was less than 0.5%, linearity was less than 0.5%, and dose rate effect was less than 0.7%. In addition the effect of dose variation from other chambers was estimated to maximum 0.8% approximately. The developed detector can be used for quality determination in output dosimetry or measurement of percentage depth dose approximately for clinical photon beam.

Analysis of Lymphocyte Subsets in Peripheral Blood after Radiotherapy / 대한치료방사선과학회지

PURPOSE: To evaluate the changes of differential counts and lymphocyte subsets in cancer patients' leukocyte before and after radiotherapy. METHODS AND MATERIALS: From Dec. 1994 to May 1995, the changes of leukocyte and its subsets in 16 patients who received radiotherapy in the Dept. of Radiation Oncology of Dong-A University Hospiatal were investigated. Radiation was delivered from 2700 cGy to 6660 cGy with median dose of 5400 cGy. The results of pre- and post-radiotherapy were analyzed by paired T-test. The results of patients who received or = 50 Gy were analyzed by wilcoxon test. RESULTS: Before and after radiotherapy, there was not any significant differences in the counts of leukocyte, granulocyte and monocyte. A remarkable decrease was noted in lymphocyte counts after radiotherapy(p=0.015). T cells, B cells and natural killer cells were also decreased in number after radiotherapy but it was not significant statistically. T helper cells and T suppressor cells were also decreased in number(p>0.05). The ratio of T helper/suppressor cell was decreased from 1.52 to 1.11 and it was significant statistically(p=0.016). The portion of T suppressor cell among all T cells was increased after radiotherapy (p=0.0195). No significant difference was observed in the analysis of leukocyte and its subsets between patients who reveived or = 50 Gy. CONCLUSION: Radiotherapy caused remarkable decrease in lymphocyte count and its subsets. Among all lymphocyte subsets, T helper cell might be the most vulnerable to radiation, considering decreased ratio of T helper/surppressor cell count after radiotherapy.

Dosimetric Characteristics of Dual Photon Energy UsingIndependent Collimator Jaws / 대한치료방사선과학회지

PURPOSE: The accurate dosimerty of independent collimator equipped for 6MV and 15MV X-ray beam was investigated to search for the optimal correction factor. METHODS AND MATERIALS: The field size factors, beam quality and dose distribution were measured by using 6MV, 15MV X-ray. Field size factors were measured from 3X3cm2 to 35X35cm2 by using 0.6cc ion chamber (NE 2571) at Dmax. Beam qualities were measured at different field sizes, off-axis distances and depths. Isodose distributions at different off-axis distance using 10X10cm field were also investigated and compared with symmetric field. RESULTS: 1) Relative field size factors was different along lateral distance with maximum changes in 3.1% for 6MV and 5% for 15MV. But the field size factors of asymmetric fields were identical to the modified central-axis values in symmetric fileld, which corrected by off-axis ratio at Dmax.2) The HVL and PDD was decreased by increasing off-axis distance. PDD was also decreased by increasing depth For field size more than 5X5cm2 and depth less than 15cm, PDD of asymmetric field differs from that of symmetric one (0.5~2% for 6MV and 0.4~1.4% for 15MV).3) The measured isodose curves demonstrate divergence effects and reduced doses adjacent to the edge close to the flattening filter center was also observed. CONCLUSION: When asymmetric collimator is used, calcutation of MU must be corrected with off-axis and PDD with a caution of underdose in central axis.